Vacuum coating system with induction heated vaporizing crucibles

ABSTRACT

A vacuum coating system having at least two separate induction heated crucibles, the crucibles being sufficiently closely spaced so that there is appreciable coupling between the two separate induction coils surrounding the crucibles. Means are provided for inducing in the tank circuit feeding each induction coil a voltage equal to and opposite to that induced in the coil by the adjacent induction coil.

United States Patent Aronson [72] Inventor: Arnold J. Aronson, Newton,Mass.

[73] Assignee: Norton Company, Worcester, Mass.

[22] Filed: 1 Feb. 10, 1971 21 Appl. No.: 114,159

[52] U.S. Cl ..219/10.75, 13/26, 219/l0.79

[51 1 Int. Cl. ..H05b 5/16 [58] Field oISearch ..2l9/l0.75,10.77, 10.79;13/26 [56] References Cited UNITED STATES PATENTS 2,935,589 5/1960 Baeuet a]. ..219/l0.75 X

VACUUM COATING SYSTEM WITH INDUCTION HEATED VAPORIZIN G CRUCIBLES [1513,657,506 1451 Apr. 18,1972

1,828,291 10/1931 Northr 3,414,659 12/1968 Kennedy ..219/l0.75 X3,472,941 10/1969 Floymayr ..2l9/l0.75 X

Primary Examiner-J. D. Miller I Assistant Examiner-B. A. ReynoldsAttorney-Oliver W. Hayes and Jerry Cohen ABSTRACT A vacuum coatingsystem having at least two separate induction heated crucibles, thecrucibles being sufficiently closely spaced so that there is appreciablecoupling between the two separate induction coils surrounding thecrucibles. Means are provided for inducing in the tank circuit feedingeach induction coil a voltage equal to and opposite to that induced inthe coil by the adjacent induction coil.

3 Claims, 1 Drawing Figure PATENTEDAPR 18 m2 INVENTOR.

, ARNOLD J. ARONSON The present invention relates to the vacuum coatingart wherein a material such as aluminum is heated to vaporizingtemperature in a vacuum chamber and the vapors are then condensed on asubstrate which is moved past the source of vapors. In presentcommercial vacuum coating apparatus for aluminizing (for example) largeareas of flexible substrate such as Mylar, it is common practice toprovide a number of crucibles containing a sufficient charge of aluminumso as to permit the coating of thousands of linear feet of the substratein a single coating run. In such apparatus, it is often extremelyimportant that the coating be very uniform and not have appreciablevariation across the width of the substrate. In order to achieve suchuniformity, it is necessary that the aluminum charge in each crucible beessentially at the same temperature. It is also important that thecrucibles be positioned rather close together so that the vapor patternsfrom the crucibles overlap to give essentially uniform concentration ofvapors impinging on the substrate at any point across the substratewidth.

In the past, one satisfactory method of providing this uniformity hasbeen that disclosed in the Baer et al. U.S. Pat. No. 2,935,589, whereina single turn coil surrounds a plurality of crucibles rather closelyspaced. The disadvantage of this arrangement, however, is that it doesnot permit the adjustment of the amount of power fed to each crucible tocompensate for problems of crucible mounting, differences in cruciblematerials, differences in degree of insulation and other factors whichcan affect the coupling of the coil and the individual crucible.Accordingly, if one of the crucibles is operating at a slightlydifferent temperature than the others because of a difference in heatbalance or coupling, there is nothing basically that can be done duringthe course of the operation to change the power input to themalfunctioning crucible. While attempts have been made to have separateinduction coils surrounding each crucible, these have not, in the past,achieved any commercial success due to the difficulty of preventingsubstantial interaction between the individual coils.

Accordingly, it is a principal object of the present invention toprovide an induction heated vacuum coating system which provides theflexibility of operation obtainable with an individually poweredinduction coil for each crucible while permitting stable operation ofthe total system by providing a simple method of eliminating the effectof coupling between adjacent separate induction coils.

In considering the present invention, it is simpler to discuss a coatingsystem containing only two separate induction coils, while obviously theprinciples of the present invention are equally applicable to systemshaving three or more separate induction heated sources. In the presentinvention, each coil has its own source of power and its own tuned tankcircuit which is tuned to the frequency of the alternating power supplyto provide high amperage, low voltage, current in each induction coil.Typically, the currents will run on the order of 800 amps for athree-turn coil. The first coil during operation will induce a strongvoltage in the second coil. In the present invention, the currentflowing in the first tank circuit also flows through a coupling meanswhich is arranged to induce in the second tank circuit a voltage equalto and opposite to that induced in the second coil by the currentflowing through the first coil. Thus, as the power is raised or loweredin the first tank circuit to adjust the temperature in the firstcrucible, for example, the current flowing in the first tank circuitchanges. This changes the amount of voltage induced in the second coiland also changes the amount of the balancing voltage induced in thesecond tank circuit by the coupling means, thus providing neutralizationof the coil-to-coil coupling despite individual adjustment of the powerlevel in each coil.

Referring to the FIGURE for a more detailed description of theinvention, there is illustrated in a very schematic, diagrammaticfashion one preferred embodiment of the invention as a pplied to twoseparately heated crucibles. In this FIGURE t e dotted line 8 representsa vacuum coating chamber, for example of the type shown in U.S. Pat. No.to Eng, 2,996,037, which patent shows three separate inductively heatedcrucibles.

In the figure, the first crucible 10 is shown in dotted lines as beingsurrounded by induction coil 12 which is energized from a variable powersupply 14 connected to a source of high frequency (e.g., 10,000 Herz)alternating power 15. In series with induction coil 12 is a condenser16, this condenser being schematically indicated as a single condenser,but obviously it may be a plurality of condensers and may be adjustablefor fine tuning of the tank circuit comprising the coil 12 and thecondenser 16. Also in series with the tank circuit is a second coil 18positioned outside of the vacuum chamber 8. The second crucible 10a issurrounded by a second coil 12a having its own variable power supply14a, power source 15a, condenser 16a and external coupling coil 18a.

In constructing the system briefly outlined above, the coupling coils 18and 18a are designed so that each induces into the other tank circuit avoltage equal to and opposed to the voltage induced in the other tankcircuit by its own series related induction heating coil. Thus, theexternal coil 18 induces into the coil 18a a voltage equal to andopposed to the voltage induced in induction heating coil 12a byinduction coil 12. The relationships between these coils can be roughlycalculated by using generally accepted design criteria. The actualcoupling can be adjusted by the spacing between the coils 18 and 18a, orby other techniques well known to those skilled in the art.

With the above described system, the power fed to each individualcrucible can be rather widely varied without adversely affecting thepower level of the adjacent crucible, thus permitting careful control ofthe coating process.

While only two crucibles have been illustrated, three or more may beequally used, in which case the various coupling means 18 and 18a e'tc.,are arranged to provide for the generation of counterbalancing voltagesin the adjacent tank circuits. As a practical matter, the adjustment isonly necessary for the immediately adjacent tank circuits, since moredistant tank circuits are only insignificantly affected by the remoteinduction coils surrounding the remote crucibles. Similarly, whileseparate sources of power have been illustrated at 15 and 15a, these canbe taken from the same alternating power source, such as a motorgenerator set.

Since certain changes can be made in theabove apparatus withoutdeparting from the scope of the invention herein involved, it isintended that all matter contained in the above description shall beinterpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a vacuum coating system wherein two individual crucibles areheated by two separate induction coils to heat the contents of thecrucibles to vaporization temperature and to provide coating of asubstrate passing over the crucibles, wherein the two crucibles arepositioned sufficiently close to each other that appreciable couplingoccurs between the two coils and wherein each coil has its own tunedtank circuit, the

improvement which comprises coupling means in the first second coil avoltage equal to tank circuit separate from the first coil and in serieswith the first coil and arranged to induce in the tank circuit of theand opposite to that induced in the second coil by the first coil.

2. The system of claim 1 wherein the second tank circuit includes asimilar coupling means for inducing into the first tank circuit avoltage equal and opposite to the voltage induced in the first coil bythe second coil.

3. The system of claim 1 wherein the two tank circuits are connected toseparate power supplies.

1. In a vacuum coating system wherein two individual crucibles areheated by two separate induction coils to heat the contents of thecrucibles to vaporization temperature and to provide coating of asubstrate passing over the crucibles, wherein the two crucibles arepositioned sufficiently close to each other that appreciable couplingoccurs between the two coils and wherein each coil has its own tunedtank circuit, the improvement which comprises coupling means in thefirst tank circuit separate from the first coil and in series with thefirst coil and arranged to induce in the tank circuit of the second coila voltage equal to and opposite to that induced in the second coil bythe first coil.
 2. The system of claim 1 wherein the second tank circuitincludes a similar coupling means for inducing into the first tankcircuit a voltage equal and opposite to the voltage induced in the firstcoil by the second coil.
 3. The system of claim 1 wherein the two tankcircuits are connected to separate power supplies.